Stupid question

I am new to DMT and have been microdosing with 1 8 second puff on a 2ml cartridge with 1g dissolved held in for 8 seconds but when I go for my second puff my chest goes numb and I start to panic.

Is this normal or is there a way to get past this fear and panic over my breathing? I am using it because I read it was good for PTSD. I can handle the head part easy. I'm really enjoying the visuals and auditory side of things but I really want to get past this and experience the full blown trip.

Has anyone any advice on how to get through this?